Generally, heterogeneous substrates are used for growth of nitride-based semiconductor layers in a viewpoint of economic feasibility. For example, sapphire substrates are widely used for growth of nitride-based semiconductor layers. In a nitride-based semiconductor layer grown on a heterogeneous substrate, strain can be generated due to a difference in lattice constant between the substrate and the growth layer, thereby causing crystal defects. In particular, treading dislocation causes current leakage and weak electrostatic characteristics, thereby causing deterioration in reliability of a semiconductor light emitting device.